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FreeBSD-SA-22:01.vt                                         Security Advisory
                                                          The FreeBSD Project

Topic:          vt console buffer overflow

Category:       kernel
Module:         vt
Announced:      2022-01-11
Credits:        Oleg Bulyzhin
Affects:        FreeBSD 12.2 and FreeBSD 13.0
Corrected:      2021-09-22 18:41:00 UTC (stable/13, 13.0-STABLE)
                2022-01-11 18:15:03 UTC (releng/13.0, 13.0-RELEASE-p6)
                2021-09-25 18:15:49 UTC (stable/12, 12.2-STABLE)
                2022-01-11 18:33:21 UTC (releng/12.2, 12.2-RELEASE-p12)
CVE Name:       CVE-2021-29632

For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:https://security.FreeBSD.org/>.

I.   Background

FreeBSD's system console is provided by the vt(4) virtual terminal console
driver.

II.  Problem Description

Under certain conditions involving use of the highlight buffer while
text is scrolling on the console, console data may overwrite data
structures associated with the system console or other kernel memory.

III. Impact

Users with access to the system console may be able to cause system
misbehaviour.

IV.  Workaround

No workaround is available.

V.   Solution

Upgrade your vulnerable system to a supported FreeBSD stable or
release / security branch (releng) dated after the correction date,
and reboot.

Perform one of the following:

1) To update your vulnerable system via a binary patch:

Systems running a RELEASE version of FreeBSD on the amd64, i386, or
(on FreeBSD 13 and later) arm64 platforms can be updated via the
freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install
# shutdown -r +10min "Rebooting for a security update"

2) To update your vulnerable system via a source code patch:

The following patches have been verified to apply to the applicable
FreeBSD release branches.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

# fetch https://security.FreeBSD.org/patches/SA-22:01/vt.patch
# fetch https://security.FreeBSD.org/patches/SA-22:01/vt.patch.asc
# gpg --verify vt.patch.asc

b) Apply the patch.  Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch

c) Recompile your kernel as described in
<URL:https://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
system.

VI.  Correction details

This issue is corrected by the corresponding Git commit hash or Subversion
revision number in the following stable and release branches:

Branch/path                             Hash                     Revision
- -------------------------------------------------------------------------
stable/13/                              9352de39c3dc    stable/13-n247428
releng/13.0/                            3e0a1e124169  releng/13.0-n244773
stable/12/                                                        r370674
releng/12.2/                                                      r371491
- -------------------------------------------------------------------------

For FreeBSD 13 and later:

Run the following command to see which files were modified by a
particular commit:

# git show --stat <commit hash>

Or visit the following URL, replacing NNNNNN with the hash:

<URL:https://cgit.freebsd.org/src/commit/?id=NNNNNN>

To determine the commit count in a working tree (for comparison against
nNNNNNN in the table above), run:

# git rev-list --count --first-parent HEAD

For FreeBSD 12 and earlier:

Run the following command to see which files were modified by a particular
revision, replacing NNNNNN with the revision number:

# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base

Or visit the following URL, replacing NNNNNN with the revision number:

<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-29632>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-22:01.vt.asc>
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